HELP!! Ceriatone Yeti trouble

[Turd Ferguson]

A friend of mine it building a Ceriatone yeti 50 watt and has it done but needs help her is what he wrote.

Any thoughts on this problem?

well good and bad news. well maybe all bad. I did not find a variac
so i built a light bulb limiter. powered up and it did right, flicked
the light on then went down.....turned stdby to play and it stayed lit
VERY dim....so i thought it was in the bias circuit.. by the way i
changed to resistors to 43K and it was better. got the tubes to bias
at about 27mA but the higher the bias the brighter the light. when i
have it plugged into my poor mans limiter, sound comes out, albeit very
muted....no limiter no sounds! Kind of stumped? what are your
thoughts?
my plate voltage is about 460 on the tubes plates by the way
Jonnathan

[danman]

What does he mean by "stays lit"? Is he talking about the pilot light or the tubes heaters? The bias circuit shouldn't have any affect unless he is referring to the power tubes red plating. Need a little more info to help out.

[ivan H]

I think he's talking about the light bulb current limiter when he says "stays lit". Cheers

[danman]

Ok, tell him to power up with no tubes installed and take the standby off. The light bulb may flash for a quick second as the capacitors charge but then it should go dim because there is no load on the amp. Next step would be to install preamp tubes and power up again. When he switches the standby off the light should glow dimly because of the small current draw from the preamp tubes. If both of these steps go well then I usually feel ok about the amp and remove the light bulb limiter. If he is using it with the power tubes installed the bulb will glow brightly because of the higher current draw of the power tubes. Has he tried playing it without the limiter yet?

[Turd Ferguson]

Thanks guys!

Yeah, not a lot of info and bias circuit has nothing to do with that. but he did try it without the limiter and it has no sound. he said that V1 and V2 voltage are not what they are supposed to be. F3 pin 9 has like 2.2 DC volts and F4 pin 4/5 has 0.4mV they are the heater that come off the small PCB board and go to a 7806 voltage regulator here is the layout of the amp.
http://ceriatone.com/images/layoutPic/H ... Yeti50.jpg
I think the problem is when he wired that up the small PCB or something is wired backwards on the voltage regulator.

[danman]

I just took a look at the schematic and I have to admit that I'm not the most qualified person to diagnose this one. Never dealt with DC heaters before. Maybe someone else with a little more experience will chip in on this one.

[ivan H]

Hi, F4, which is pins 4 & 5 of the 1st & 2nd pre amp tubes is actually grounded. If u check the schematic u will see it is connected to go the grounded center leg of the 7806 regulator. F3, being pins 9 of both pre amp tubes, is connected to the filtered (4700uf electrolytic) output of the 7806 regulator, so it should have 6VDC on them. The regulator requires an input voltage at least a few volts higher than the intended output voltage. This is achieved by rectifying the PT's 5VAC winding with a voltage doubling type rectifier comprising two 4700 uf electrolytics wired in series, paralleled with two diodes wired in series. One side of the 5VAC winding connects to the junction of the two electrolytics, the other side of the 5VAC winding connects to the junction of the two diodes. The rectifier feeds the input of the 7806 regulator (1st leg) & should have around 11VDC, or a little more on it. Hope this is of some help. Cheers

[Turd Ferguson]

Thanks!! I will keep ya updated